Prostheses are wellknown for implantation in the body to replace removed tissue or to augment tissue already present. The objective is to provide a prothesis which will not be rejected by the body, and which after implantation will provide an improved visual configuration, and with it a tactile response which is close to that which arises from a normal body element, for example the female breast.
A well-known and generally successful prosthesis of this type has a relatively thin and quite flexible envelope made of vulcanized (cured) silicone elastomer. It is usually filled either with a silicone gel or with a normal saline solution. Because of the tendency of either of these fluids to pass through the envelope over a long period of time--even though it is an extremely slow process relating to limited semi-permeability, saline is preferred. Saline solutions do not adversely affect the tissues, while silicone gels can in some instances be troublesome.
As is so often the case, the improvement of one problem can give rise to another. A gel-filled prosthesis tends to hold its shape better than a saline filled envelope, assuming identical envelopes. This is in the sense of resisting tight bends and folds of the envelope material. Acceptably thin silicone envelopes are prone to splitting or to excess leakage if they are strongly folded. A saline solution provides little resistance to this folding, especially in comparison to an envelope filled with a gel where the gel, being more viscous, offers some resistance. Of course the tendency to break or to leak can be reduced by increasing the wall thickness of the envelope, but there comes a point where the gross properties of the prosthesis are then changed to an unacceptable degree, for example by an excessive loss of flexibilty which results in a structure that when palpated clearly includes a foreign structure. This deprives the patient of a very important advantage of a proper prosthesis.
Accordingly it is an object of this invention to provide a prosthesis to contain aqueous, usually saline, solutions, but which while retaining many of the textural and flexure properties of a conventional prosthesis, has a composite wall that is resistant to sharp folding.